This invention relates to gas turbine engine blades and, more particularly, to an improved tip cap configuration for a cooled turbine blade. It is well known that gas turbine engine efficiency is, at least in part, dependent upon the extent to which hot expanding combustion gases in the turbine leak across a gap between turbine blades and seals or shrouds which surround them. The problem of sealing between such cooperating members is very difficult in the turbine section because of high temperatures and centrifugal loads. One method of improving the sealing between the turbine blade and seal or shroud is the use of squealer tips such as those shown in U.S. Pat. Nos. 4,540,339 and 4,247,254, the disclosures of which are herein incorporated by reference. Other tip arrangements have been used including flat blade tip surfaces facing the shroud. Blade tips because they are often abrasively worn down during engine operation have been made removable in order to prolong the life of the remaining portion of the blade. Cooling of the turbine blades is required in modern gas turbine engines because of the very high temperatures involved. Therefore, various types of hollow blades or blades with air passages contained within have been designed to cool the walls of the turbine blade.
A variety of configurations for tip caps for the type of hollow turbine blades used in modern gas turbine engines have been developed. During operation of a gas turbine engine, interference between such relatively rotating blade tips and surrounding shrouds or seals causes heating of the blade tip resulting in excessive wear or damage to the blade tips and shrouds or seals. Temperature changes create differential rates of thermal expansion and contraction on the rotor and shroud which may result in rubbing between the blade tips and shrouds. Centrifugal forces acting on the blades and structural forces acting on the shroud create distortions thereon which may also result in rubs. It is, therefore, desirable to cool the blade tips. In the case of squealer type tips augmented heating occurs in the cavity between the walls of the squealer tip which requires additional cooling. Because of the complexity and relative high cost of replacing or repairing the blades, it is desirable to prolong the life of the blade tips and respective blades as long as possible. Blade tip cooling holes are known in the art as shown in U.S. Pat. No. 4,247,254 and as applied to squealer tips in U.S. Pat. No. 4,540,339. Turbine blade designers and engineers are constantly striving for more efficient means of cooling the turbine blade tips. Cooling air used to accomplish this is expensive in terms of overall fuel consumption and therefore more efficient means of cooling improves the efficiency of the engine thereby lowering the engine's operating cost. Turbine blade designers and engineers are also striving to design more effective means of cooling the turbine blade tips in order to prolong turbine blade life and thereby again reducing the engine's operating cost.